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Two photon reconstruction with ECAL and low mass background

Two photon reconstruction with ECAL and low mass background Alexei Stavinskiy, Konstantin Mikhaylov ITEP, Russia. A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 1. Input.

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Two photon reconstruction with ECAL and low mass background

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  1. Two photon reconstruction with ECAL and low mass background Alexei Stavinskiy, Konstantin Mikhaylov ITEP, Russia A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 1

  2. Input 2*104 central UrQMD events AuAu@25AGeV (Local analysis) Full ECAL reconstruction (version of February 2009) with CBM root January 2009 version (version with new geometry) Cuts: Minimal energy deposited in ECAL 500 MeV. χ2 (of photon reconstruction) < 3. Minimal distance between cluster (DBC) > 20 cm. Particles from target = Vz < 1cm (conventional) A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 2

  3. WA 98 experiment [arXiv:nucl-ex/0006007] A low mass tail on the π0 was observed. The tail can result from π0 produced downstream from target: • from decays (K0s, ...)‏ • from background interaction on downstream materials (the normalized target out background contribution is shown by the open circles In part c)) A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 3

  4. 1t 1b θb θt 2b πtarget πbackground 2t • Differences between target and background pairs: • *mean photon energy higher for target photons *real emission angle difference for target photons from π(η) decay corresponds to measured invariant mass; this is not the case for background pairs • *vertex position is fixed for target pairs; • for background pairs vertex position distribution • corresponds to detectors (support) position A.Stavinskiy K.Mikhailov ITEP CBM collaboration meeting, March 2009 4

  5. Mγγsame mother A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 6

  6. Mγγ vs Vz π0 ECAL RPC TRD3 TRD2 TRD1 RICH A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 7

  7. π0 mothers vs Vz For 0 with Vz>1. mothers: code % production -321 1.9%  K- ->pi-pi0 cτ=3.7m -211 22.1%  pi- 130 2.2%   KL0 ->pipipi0 cτ=15.34m 211 14.5%   pi+ 310 22.2%   Ks0 ->pi0pi0 cτ=2.7m 321 4.5%   K+    ->pi+pi0 cτ=3.7m 2112 11.9% n 2212 10.9% p 3122 5.6% Lambda->npi0 cτ=7.8cm 3222 3.6% Sigma+ ->ppi0 cτ=2.4cm 3322 0.4% Xi0->Lambdapi0 cτ=8.7cm Vz PDG code A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 8

  8. Pi0 mothers vs Vz K- π- π+ KL0 K+ n p Σ+ Ξ0 KS0 Λ A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 9

  9. XYECAL for different VZ Materials X0 A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 10

  10. Ecut: π0 Z-vertex vs Mγγ A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 11

  11. Ecut Rcut: Mγγ,same mother S/B for 0<Mγγ<200MeV A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 12

  12. Ecut Rcut: Mγγ,same mother S/B for 0<Mγγ<120MeV A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 13

  13. DBC cut: Mγγ,same mother Distance Between Clusters>20cm Distance Between Clusters>50cm A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 14

  14. DBC > 50 cm, Ecut Rcut S/B for 0<Mγγ<120MeV A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 15

  15. Signal and Background K.Mikhaylov ITEP CBM collaboration meeting, March 2009 16

  16. Signal-Background VZ<1cm S/sqrt(S+B)=20 S/B=0.25% K.Mikhaylov ITEP CBM collaboration meeting, March 2009 17

  17. Correlation function (S/B) K.Mikhaylov ITEP CBM collaboration meeting, March 2009 18

  18. Correlation function (S/B) VZ<1cm K.Mikhaylov ITEP CBM collaboration meeting, March 2009 19

  19. A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 20

  20. Two-photon correlations e+ 2 2rec 1 1 e- • External conversion: • No close cluster interference • No hadron contamination C2 calculated in EMCAL and converted+EMCAL agree => both effects are under control A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 21

  21. Measurement of Direct Photons via Conversion in CBM Melanie Klein-Bosing WWU Munster,Germany CBM Collaboration Meeting, Dubna 2008, October

  22. Conclusions • The feasibility of π and η meson identification with ECAL was shown • The low mass background in two photon invariant mass was studied • Two main contribution to the low mass background are: • Interaction with downstream detector construction • Decay of long lived particles • Possible cuts to reduce (slightly) low mass background: • Cut on gamma energy • Cut on distance between center of clusters • Other possible ways: • Background simulations • Combined photon pair identification with different detectors

  23. Extra slides

  24. 1t e1b 2t πtarget e2b Possible source of low mass background A.Stavinskiy K.Mikhailov ITEP CBM collaboration meeting, March 2009 25

  25. R-dependence A.Stavinskiy, K.Mikhailov ITEP CBM collaboration meeting, March 2009 26

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